[amsat-bb] Re: ISS Bounce on 1296 MHz
Hi Domenico, Thanks for your interest in the ISS reflections Now about your questions. 1. I started calling Andreas as soon as my dish could see ISS. That was on May 23 at 8 degrees elevation. So the distance would have been close to 2000 km at that time. Andreas reports that he heard me right from the beginning! Own echo's is not possible because the time is too short 2. We heard the strongest signals when ISS was right overhead. In my case that was at about 60 degrees elevation. Distance probably somewhere around 500 km? On the SDR recording from Andreas we can see the signal peaking 20 dB over the noise and sometimes even a bit more. 3. We both used analog CW but we both listened in the SSB passband (approx. 2.5 kHz) to have some margin of error is case our Doppler compensation was not 100% OK. But once I found Andreas I did not touch the RIT of my rig anymore during the QSO. Doppler compensation worked fantastic! We hope to try other modes in future. FSK441 but also JT65 in 30 sec period mode, and when ISS is overhead probably SSB is possible I am also involved in the restoration of the 25 m Dwingeloo dish PI9CAM (see www.camras.nl) And the dish will be on air in a few months from now (I hope) We hope to experiment with passive satellite reflection there. ISS will be the start and with the dish having 48 dB gain it will be possible with QRP But maybe it's possible with other low orbiting satellites too To be continued! 73! Jan PA3FXB Hello Jan, PA3FXB It is very interesting that you heard the strongest signals when the ISS was right overhead and that in your case that was at about 60 degrees elevation with distance from the ISS somewhere around 500 km and that in the SDR recording from Andreas you can see the signal peaking +20 dB over the noise and sometimes even a bit more. It is also interesting that both of you were using analog CW and both listened in the SSB passband (approx. 2.5 kHz) As you can see looking at my previous budged calculations the expected S/N ratio on CW was +6.9 dB using a receiving bandwidth of 500 Hz on CW It is possible that my calculations showed a less level in ratio S/N = +6.9 dB in comparison to your received +20 dB because for calculation with the RADAR equation I have used a reflection factor for the ISS of only 10% wich in reality is very low because for the Moon we use a reflection factor of 7% but the Moon is made of stone and not a metallic reflecting object like the ISS. Considering that the ISS is made almost of metallic structural material as well for supporting the solar panels and considering that the efficiency of a metallic parabolic dish is never better than 50% I have uptodate my previous link budged calculation using a reflection factor of 50% for the ISS and as you can read belove the S/N ratio at a distance of 700 km jumped up to +17dB over the noise ! This means that your experimental investigation receiving +20 dB match well with my calculation showing +17 dB and for the future we can consider that a reflection factor for the ISS of 50% is a real figure to be used. Since you live in a quite location the antenna temperature at 1296 MHz when aimed toward the Cold Sky can be only 5 degrees kelvin instead of the previously estimated 50 degrees kelvin so that the overall Noise Floor of your receiving system decreases by 3.29 dB Read please the following revised calculations using a ISS reflection factor of 50% instead of 10% at a range of 700 km and 5 degrees kelvin for the equivalent antenna temperature Ta instead of 50 kelvin LINK BUDGED CALCULATIONS by i8CVS We consider the ISS like a passive reflector with reflectivity factor of 50 % to try a QSO by reflection Earth-ISS-Earth DATA: 1) The solar panels of the ISS plus the central body large like a Boeing 747 have a metallic reflecting surface of about 2000 square meters and we consider the ISS like a circular RADAR target having being a metallic plate an estimated reflectivity factor S of 50 % at SHF 2) The range EARTH-ISS at elevation of 35 degrees is about 700 km 3) Our EME station at 1296 MHz uses a 3 meters dish in diameter with gain of 29 dB and 200 W at the feed 4) The overall noise figure of our receive system is NF = 0.5 dB while the antenna temperature is 5 kelvin when pointed at the Cold Sky and we receive on CW using a filter with a BW large 500 Hz 5) We use only analogic reception without digital software like WSJT or similar tecniques. CALCULATION PROCEDURE : Aiming the dish towards the ISS when distant 700 km and transmitting on CW and using the RADAR equation we calculate the Signal to Noise ratio S/N to see if on CW the echoes reflected by the ISS are above or belove the Noise Floor of receiver. First of all using the RADAR equation we calculate the round trip attenuation in dB between EARTH-ISS-EARTH when
[amsat-bb] Re: ISS -Bounce on 1296 MHz ( easy calculation using RADAR equation )
- Original Message - From: Jan van Muijlwijk To: i8cvs Sent: Friday, May 31, 2013 9:51 AM Subject: Re: .[amsat-bb] Re: International Space Station-Bounce on 1296 MHz Hi Domenico, Thanks for your interest in the ISS reflections Now about your questions. 1. I started calling Andreas as soon as my dish could see ISS. That was on May 23 at 8 degrees elevation. So the distance would have been close to 2000 km at that time. Andreas reports that he heard me right from the beginning! Own echo's is not possible because the time is too short 2. We heard the strongest signals when ISS was right overhead. In my case that was at about 60 degrees elevation. Distance probably somewhere around 500 km? On the SDR recording from Andreas we can see the signal peaking 20 dB over the noise and sometimes even a bit more. 3. We both used analog CW but we both listened in the SSB passband (approx. 2.5 kHz) to have some margin of error is case our Doppler compensation was not 100% OK. But once I found Andreas I did not touch the RIT of my rig anymore during the QSO. Doppler compensation worked fantastic! We hope to try other modes in future. FSK441 but also JT65 in 30 sec period mode, and when ISS is overhead probably SSB is possible I am also involved in the restoration of the 25 m Dwingeloo dish PI9CAM (see www.camras.nl) And the dish will be on air in a few months from now (I hope) We hope to experiment with passive satellite reflection there. ISS will be the start and with the dish having 48 dB gain it will be possible with QRP But maybe it's possible with other low orbiting satellites too To be continued! 73! Jan PA3FXB Hello Jan, PA3FXB It is very interesting that you heard the strongest signals when the ISS was right overhead and that in your case that was at about 60 degrees elevation with distance from the ISS somewhere around 500 km and that in the SDR recording from Andreas you can see the signal peaking +20 dB over the noise and sometimes even a bit more. It is also interesting that both of you were using analog CW and both listened in the SSB passband (approx. 2.5 kHz) As you can see looking at my previous budged calculations the expected S/N ratio on CW was +6.9 dB using a receiving bandwidth of 500 Hz on CW It is possible that my calculations showed a less level in ratio S/N = +6.9 dB in comparison to your received +20 dB because for calculation with the RADAR equation I have used a reflection factor for the ISS of only 10% wich in reality is very low because for the Moon we use a reflection factor of 7% but the Moon is made of stone and not a metallic reflecting object like the ISS. Considering that the ISS is made almost of metallic structural material as well for supporting the solar panels and considering that the efficiency of a metallic parabolic dish is never better than 50% I have uptodate my previous link budged calculation using a reflection factor of 50% for the ISS and as you can read belove the S/N ratio at a distance of 700 km jumped up to +17dB over the noise ! This means that your experimental investigation receiving +20 dB match well with my calculation showing +17 dB and for the future we can consider that a reflection factor for the ISS of 50% is a real figure to be used. Since you live in a quite location the antenna temperature at 1296 MHz when aimed toward the Cold Sky can be only 5 degrees kelvin instead of the previously estimated 50 degrees kelvin so that the overall Noise Floor of your receiving system decreases by 3.29 dB Read please the following revised calculations using a ISS reflection factor of 50% instead of 10% at a range of 700 km and 5 degrees kelvin for the equivalent antenna temperature Ta instead of 50 kelvin The following calculation is easyer than the previous one because uses directly the RADAR equation. LINK BUDGED CALCULATIONS by i8CVS We consider the ISS like a passive reflector with reflectivity factor of 50 % to try a QSO by reflection Earth-ISS-Earth DATA: 1) The solar panels of the ISS plus the central body large like a Boeing 747 have a metallic reflecting surface of about 2000 square meters and we consider the ISS like a circular RADAR target having being a metallic plate an estimated reflectivity factor S of 50 % at SHF 2) The range EARTH-ISS at elevation of 35 degrees is about 700 km 3) Our EME station at 1296 MHz uses a 3 meters dish in diameter with gain of 29 dB and 200 W at the feed 4) The overall noise figure of our receive system is NF = 0.5 dB while the antenna temperature is 5 kelvin when pointed at the Cold Sky and we receive on CW using a filter with a BW large 500 Hz 5) We use only analogic reception without digital software like WSJT or similar tecniques. CALCULATION PROCEDURE : Aiming the dish towards the ISS when distant 700 km and transmitting on CW and using the RADAR
